Kulkarni et al., Chem. Mater. 2004, 16, 4556-4573 (the contents of which are incorporated herein by reference) have reviewed the literature concerning electron transport materials (ETMs) used to enhance the performance of OLEDs. In addition to a large number of organic materials, they discuss metal chelates including aluminium quinolate, which they explain remains the most widely studied metal chelate owing to its superior properties such as high EA (˜−3.0 eV; measured by the present applicants as −2.9 eV) and IP (˜−5.95 eV; measured by the present applicants as about −5.7 eV), good thermal stability (Tg˜172° C.) and ready deposition of pinhole-free thin films by vacuum evaporation. Aluminium quinolate remains a preferred material both for use as a host to be doped with various fluorescent or phosphorescent materials to provide an electroluminescent layer and for use as an electron transport layer. It is an object of the invention to provide additional electron transport materials that provide alternatives to aluminium quinolate when used in an electron transport layer e.g. of an OLED and that may in some embodiments provide superior performance in at least some respects e.g. greater current density at a given voltage.